Steven Bethard <[EMAIL PROTECTED]> writes:
Mike C. Fletcher wrote:
[...]
>>> def changes( dataset ): ... last = None ... for value in dataset: ... if value != last: ... yield value ... last = value ... >>> print list(changes(data )) which is quite readable/elegant IMO.
But fails if the list starts with None:
py> lst = [None,0,0,1,1,1,2,2,3,3,3,2,2,2,4,4,4,5] py> def changes(dataset): ... last = None ... for value in dataset: ... if value != last: ... yield value ... last = value ... py> list(changes(lst)) [0, 1, 2, 3, 2, 4, 5]
A minor modification that does appear to work:
py> def changes(dataset): ... last = object() ... for value in dataset: ... if value != last: ... yield value ... last = value ... py> list(changes(lst)) [None, 0, 1, 2, 3, 2, 4, 5]
Unless the first object in the list has a weird __cmp__ (does happen...). OK, weird __cmp__s are nasty anyway, but still, why compound it through cleverness when you can write a really plodding function that *always* does what it says on the tin?
In that case:
Py> def collapsed(iterable): ... itr = iter(iterable) ... last = itr.next() ... yield last ... for value in itr: ... if value != last: ... yield value ... last = value ... Py> from Tkinter import _flatten #** Py> lst = list(_flatten([[i] * 5 for i in range(10)])) Py> lst [0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 3, 4, 4, 4, 4, 4, 5, 5 , 5, 5, 5, 6, 6, 6, 6, 6, 7, 7, 7, 7, 7, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9] Py> list(collapsed(lst)) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
** Hmm, this function really is quite handy when generating test data. Maybe in Python 2.5 the line should be spelt "from itertools import flatten"
Cheers, Nick.
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Nick Coghlan | [EMAIL PROTECTED] | Brisbane, Australia
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http://boredomandlaziness.skystorm.net
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